Comparison of the molecular dynamics of celluloses and related polysaccharides in wet and dried states by means of dielectric spectroscopy

Abstract

The dielectric relaxation spectra of polysaccharides are already affected very specifically by small amounts of water. The measured samples of cellulose, starch and dextran behave differently in the wet and in the dried state comparing their low temperature dielectric spectra: The positions of the secondary relaxation in the frequency scale, which are due to the local chain mobility, shift in a specific manner between wet and dried state for every substance. In general, we can say that drying strongly decreases the relaxation strength for all samples. The dielectric spectra of the wet polysaccharides (2 to 12% w/w water content) show an additional relaxation process (βwet-relaxation) in the room temperature range (0°C to 60°C) which vanishes after an intensive drying procedure. The experimental results were fitted by using the Havriliak-Negami-equation for each individual relaxation process. This evaluation leads to a number of physical parameters for the polymer dynamics given in the paper. The results could be explained by the differences in the interaction of the several polysaccharides with water caused by their distinct glycosidic linked backbones and their different supramolecular structures.